In order to reduce a wiring delay in a semiconductor device, it is considered to use organic material having a low dielectric constant for an inter-layer insulating film. Hydrocarbon-based polymer such as divinyl-siloxane benzo cyclobutene (BCB) polymer, poly-phenylene, polyallyere ether, polyallylene, and organic silica such as methyl silica are the organic materials suitable for the inter-layer insulating film. In order to further reduce effective dielectric constant, it is considered to use organic silica with a porous structure for the interlayer insulating film. Such a technique is disclosed in, for example, “Dependency of Basic Properties of Porous Silica ILD Thin Films in the k Range 1.6-2.7 on CMP Compatibility”, H. Hanahata et sl., (Conference Proceedings ULSI XVI, 2001, Materials Research Society, P. 629).
In order to use the organic low dielectric constant material for the inter-layer insulating film, it is necessary to process an organic film made of the organic low dielectric constant material. For this reason, the development of an organic film processing technique has been advanced.
A first conventional technique for the organic film processing intended to avoid shape abnormality such as undercut and bowing, and to process the organic low dielectric constant material film into a predetermined shape is disclosed in Japanese Laid Open Patent Application (JP-P2000-36484A). In the first conventional organic film processing technique, a mixed gas of hydrogen atoms containing gas and nitrogen atoms containing gas is used as an etching gas for the organic low dielectric constant material film. The usage of the mixed gas of the hydrogen atoms containing gas and the nitrogen atoms containing gas improves the anisotropy of etching, and avoids the shape abnormality such as the undercut and the bowing. The first conventional technique further discloses that when poly-organo-siloxane bridge bis-benzo-cyclobutene is used as the organic low dielectric constant material, oxygen gas and difluoro methylene are added to the above-mentioned mixed gas.
Moreover, a second conventional technique for the organic film processing intended to improve the etched shape of the organic low dielectric constant material film and to prevent the deterioration in the film quality of the organic low dielectric constant material film is disclosed in Japanese Laid Open Patent Application (JP-P2001-35832A). In the second conventional technique, the mixed gas of a first gas containing one or both of hydrogen atoms and nitrogen atoms and a second gas in which phoshor, sulfur or silicon atoms are easily separated is used as an etching gas of the organic low dielectric constant material film. Oxygen from the etching gas is removed so as to protect the deterioration in the film quality in the organic low dielectric constant material film. When this mixed gas is used to etch the organic low dielectric constant material film, the phoshor, sulfur or silicon atoms are deposited on the sidewall of a pattern generated through the etching and polymerized to form a sidewall protection film. Due to the formation of the sidewall protection film, the second conventional technique enables the organic low dielectric constant material film to be anisotropically etched. The second conventional technique further discloses that since a nitrogen gas is added to the mixed gas serving as the etching gas, nitrogen is added to the formed sidewall protection film, thereby forming the stronger sidewall protection film.
Moreover, a third conventional technique for the organic film processing intended to provide an anisotropic etching method of the organic low dielectric constant material film with plasma is disclosed in Japanese Laid Open Patent Application (JP-P2000-269185A). In the third conventional technique, a mixed gas of oxygen gas and ammonium, a mixed gas of oxygen gas and water, a mixed gas of oxygen gas and methane and a mixed gas of oxygen gas and hydrogen gas are used as an etching gas. The usage of the etching gas as mentioned above enables a passivation layer to be formed on a sidewall of a pattern and enables anisotropic etching. The third conventional technique further discloses that a small rate of nitrogen may be arbitrarily added to the gas.
Moreover, a fourth conventional technique for the organic film processing intended to protect the organic low dielectric constant material and to keep the entire effective low dielectric constant of a device is disclosed in Japanese Laid Open Patent Application (JP-P2001-351976A). In the fourth conventional technique, one layer or two layers of sacrificial hard mask and a permanent hard mask are formed on an organic low dielectric constant material film. In order to form a dual damascene structure, three layers of hard masks are formed. The one layer or two layers of the sacrificial hard mask enable the formation of the permanent hard mask. The permanent hard mask protects the organic low dielectric constant material film and avoids the change in its dielectric constant. The fourth conventional technique discloses that for the etching of the organic low dielectric constant material film, Ar of 0 to 500 scm, C4F8 of 0 to 20 sccm, C2F6 of 0 to 100 sccm, CHF3 of 0 to 100 sccm, CF4 of 0 to 100 sccm, O2 of 0 to 100 sccm, N2 of 0 to 100 sccm, CO of 0 to 100 sccm and CO2 of 0 to 100 sccm are used for an etching gas.
As a typical etching technique, Japanese Laid Open Patent Application (JP-A-Heisei 7-193049) discloses an etching apparatus that can carry out the etching without charging up. Moreover, Japanese Laid Open Patent Application (JP-P2001-351897A) discloses a plasma etching apparatus that can surely accelerate electrons. However, those etching techniques are not intended to solve the problems peculiar to the organic low dielectric constant material.